1. Field to the Invention
The present invention relates to a process and apparatus for treating fluorine-containing waste solution discharged from semiconductor plants and so forth. More particularly, the present invention relates to a waste solution treatment process and apparatus that uses a solid-liquid separation filtration membrane.
2. Description of the Prior Art
Hitherto, a process for removing fluorine from a waste solution containing hydrogen fluoride, ammonium fluoride or other fluorine compounds discharged from semiconductor plants and so forth has been carried out by adding calcium hydroxide i.e. slaked line, to the waste solution, forming insoluble calcium fluoride and then separating the solid and liquid by a filtration membrane and sedimentation. In the case of a waste solution treatment process using a solid-liquid separation filtration membrane, it was typical to employ a system that an entire volume of waste solution, is filtered.
However, in the above-mentioned prior art process, due to the susceptibility to the occurrence of decreased flux caused by clogging of the filtration membrane, it was difficult to maintain a high volume of treated solution.and the process required considerable labor for maintenance.
Accordingly, one object of the present invention is to provide a waste solution treatment process that is able to maintain a high volume of treated solution while also allowing easy maintenance.
Another object of the present invention is to provide an apparatus for carrying out the treatment process of the present invention.
The above-mentioned objects can be accomplished by adding calcium salt and an inorganic coagulant to a fluorine-containing waste solution, followed by filtering said waste solution by cross-flow filtration.
Also, after insolubilizing the fluorine in said waste solution by adding calcium salt, it is more preferable to coagulate the insolubilized fluorine by addition of an inorganic coagulant.
Further, it is preferable to use iron salt and/or aluminum salt as the inorganic coagulant, more preferably iron salt.
In addition, according to the present invention, there is provided an apparatus for treating a fluorine-containing waste solution which comprises a calcium salt feed unit that supplies calcium salt to fluorine-containing waste solution, an inorganic coagulant feed unit that supplies an inorganic coagulant to said waste solution, and a filtration unit that filters said waste solution, to which calcium salt and an inorganic coagulant have been added, with timing, by cross-flow filtration.
The apparatus may be preferably configured so that calcium salt and inorganic coagulant are supplied to a common coagulation tank to which said waste solution is supplied.
Alternatively, the apparatus may be preferably configured to have a pre-stage reaction tank and post-stage coagulation tank, in which fluorine-containing waste solution is supplied, so that the calcium salt feed unit supplies calcium salt to the reaction tank, while the inorganic coagulant feed unit supplies inorganic coagulant to the coagulation tank.